MSP430FR2355: PROBLEM WITH SPI COMMUNICATION

Your drawing seems to say you have the slave STE (P4.0) tied to 3.6V (high), which I suspect isn't your intent. Your code seems to think you've tied (slave) STE to (master) P3.6. 

How is this actually wired?

[Edit: Seeing this in bigger print, I suspect your drawing meant to say P3.6, not 3.6V.

Looking further: Your master seems to be assuming STE is active low, but the slave assumes active high (UCMODE=1). 

Also: If you're using the Launchpad, be sure to remove the RXD/TXD jumpers from J101. These affect SIMO/SOMI, not STE, but you still should do it.]

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Unsolicited:

> GPIO_setOutputLowOnPin(GPIO_PORT_P3, GPIO_PIN6);
> UCA1TXBUF = TXData; // Transmit characters
> GPIO_setOutputHighOnPin(GPIO_PORT_P3, GPIO_PIN6);

This probably de-asserts STE before the byte has shifted out, which will freeze the slave SPI (even mid-byte, as I recall). You should hold off until the byte completes, with something resembling:

> while (UCA1STATW & UCBUSY) /*EMPTY*/;  // Wait for byte to be shifted out

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> { while (!(UCB1IFG&UCTXIFG)); // USCI_B1 TX buffer ready?

I think this works by accident. It should probably be

> { while (!(UCA1IFG&UCTXIFG)); // USCI_A1 TX buffer ready?

Thanks for your answer.

I modify my program, and I can send and receive correctly in mode_ 1(STE HIGH for slave).

But I can't send and receive in mode_2 (STE LOW for slave), yet I put my IO in low output. I think the bus between STE(slave) and 3.6 stay high (I measure 1.3V when I put the output of my IO(3.6) only at low).

Why my bus is always in High ? STE in Slave put a voltage in output? I join my new code.

#include <msp430.h>
#include "gpio.h"

void main(void)
{
    WDTCTL = WDTPW|WDTHOLD;                   // Stop watchdog timer


    //Configuration SPI pins on Hardawre
    P4SEL0 |= BIT0 | BIT1 | BIT2 | BIT3;             // set 4-SPI pin as second function

    GPIO_setAsOutputPin(GPIO_PORT_P2, GPIO_PIN3); //indication alimentation
    GPIO_setOutputHighOnPin(GPIO_PORT_P2, GPIO_PIN3);

    GPIO_setAsOutputPin(GPIO_PORT_P2, GPIO_PIN4); //indication reception
    GPIO_setOutputLowOnPin(GPIO_PORT_P2, GPIO_PIN4);

    UCA1CTLW0 |= UCSWRST;                     // **Put state machine in reset**
    UCA1CTLW0 |= UCSYNC|UCMSB|UCMODE_1;         // 3-pin, 8-bit SPI slave
                                              // Clock polarity high, MSB
    UCA1CTLW0 |= UCSSEL__SMCLK;
    UCA1BR0 = 0x02;
    UCA1BR1 = 0;                              //

    UCA1CTLW0 &= ~UCSWRST;                    // **Initialize USCI state machine**

    PM5CTL0 &= ~LOCKLPM5;                     // Disable the GPIO power-on default high-impedance mode
                                              // to activate previously configured port settings
    UCA1IE |= UCRXIE;                     // Enable TX interrupt
    __bis_SR_register(GIE);       // Enter LPM0, enable interrupts
}

#pragma vector=USCI_A1_VECTOR
__interrupt void USCI_A1_ISR(void)
{   while (!(UCA1IFG&UCTXIFG));               // USCI_A1 TX buffer ready?  //erreur 15/04/24 B1->A1
    UCA1TXBUF = UCA1RXBUF;                    // Echo received data
    GPIO_toggleOutputOnPin(GPIO_PORT_P2, GPIO_PIN4);
}

#include <msp430.h> 
#include "gpio.h"

/**
 * main.c
 */

//3.6 CS
//UCA1 SPI


unsigned char TXData;
unsigned char RXData;                            // Holds TX data

int main(void)
{
	WDTCTL = WDTPW | WDTHOLD;	// stop watchdog timer
	
    P4SEL0 |= BIT3 | BIT2 | BIT1;             // set 3-SPI pin as second function

    GPIO_setAsOutputPin(GPIO_PORT_P3, GPIO_PIN6);
    GPIO_setOutputLowOnPin(GPIO_PORT_P3, GPIO_PIN6);

    GPIO_setAsOutputPin(GPIO_PORT_P2, GPIO_PIN3);

    UCA1CTLW0 |= UCSWRST;                     // **Put state machine in reset**

    UCA1CTLW0 |= UCMST|UCSYNC|UCMSB;          // 3-pin, 8-bit SPI master
                                              // Clock polarity high, MSB
    UCA1CTLW0 |= UCSSEL__SMCLK;                // Select SMCLK

    UCA1BR0 = 0x02;                           // BRCLK = SMCLK/2
    UCA1BR1 = 0;                              //

    UCA1CTLW0 &= ~UCSWRST;                    // **Initialize USCI state machine**

    TXData = 0x01;                            // Holds TX data

    PM5CTL0 &= ~LOCKLPM5;

    GPIO_setOutputHighOnPin(GPIO_PORT_P2, GPIO_PIN3);

    while(1)
    {
         UCA1IE |= UCTXIE | UCRXIE ;                     // Enable TX interrupt
        __bis_SR_register(GIE);   // enable global interrupts, enter LPM0
        //__no_operation();                     // For debug,Remain in LPM0
        __delay_cycles(10000);                 // Delay before next transmission
        TXData++;                             // Increment transmit data
    }
}



#pragma vector=USCI_A1_VECTOR
__interrupt void USCI_A1_ISR(void)
{
    switch(__even_in_range(UCA1IV,USCI_SPI_UCTXIFG))
    {
        case USCI_NONE: break;                // Vector 0 - no interrupt
        case USCI_SPI_UCRXIFG:
              RXData = UCA1RXBUF;
              UCA1IE &= ~UCRXIE;
              break;
        case USCI_SPI_UCTXIFG:
           // GPIO_setOutputLowOnPin(GPIO_PORT_P3, GPIO_PIN6);
            UCA1TXBUF = TXData;                    // Transmit characters
            while (UCA1STATW & UCBUSY) ;           /*EMPTY*/
           // GPIO_setOutputHighOnPin(GPIO_PORT_P3, GPIO_PIN6);
            UCA1IE &= ~UCTXIE;
              break;
        default: break;
    }
}

Yes, it does sound like a bus conflict (some other agent driving the wire high), but I don't see how that would happen, based on what you've posted. 

What platform are you using? Are these Launchpads?